Controlling apparatus



mpi'943k, I A. R MABEY 2,326,238

CONTROLLING APPARATUS Filed June 3, 1941 2, sheets-sheet 1 .nv mvroa 1ARTHUR R. MABY ATTORNEY Y Aug. 10, 1943.

A. R. MABEY 2,326,238

conmomme APPARATUS Filed June 5, 1941 2 Sheets-Sheet 2 INVENTOR. ARTHURR. MABE Y ATTORNEY Patented Aug. 10, 1943 cbmommo APPARATUS" Arthur R.Mabey, Waterbury, Conn, assignor to The Bristol Company, Waterbury,Conn., a corporation 01' Connecticut Application June 3, 1941','SerialNo. 396,483 6 Claims. (Ol. 74-1 )1 This invention relates to automaticcontrol devices, and more especially to an automatic control mechanismadapted for use with a measuring instrument of the self-balancingpotentiometer class, wherein it isdesired by Pneumatic or other means tomaintain at a predetermined value the magnitude of the condition whosemeasurement is efiected by the instrument.

In U. S..Letters Patent No.,2,l15,528, issued to O. H. Hunt, April26,1938, there is disclosed a method by which a pneumatic control devicemay be-rendered subject to a measuring instrument of the potentiometerclass; and this invention isdirected essentially to improvements wherebythe principles set forth in said patent may be more efiectuallyutilized, and rendered more widely applicable to meet a variety ofcontrol conditions.

It is an object of this invention to provide a compact cam-actuatedcontrol system, readily applicable to the mechanism of a self-balancingpotentiometer.

It is a further object to provide such a system I in a form which shallbe inherently free of backlash between the control and actuatingmechasible for inspection and adjustment while the mechanism remains innormal operation.

Other features and advantages of the invention will be hereinafterdescribed and claimed.

In the accompanying drawings:

Fig. 1 is an isometric representation of an instrument embodying theprinciples of the invention.

Fig. 2 is a diagrammatic representation of a complete installationincluding the instrument.

tion of the principles of the invention to temper-' ature control bypneumatic means, 10 designates a, framework upon which are mounted'aselfbalancing potentiometer mechanism, a pneumatic control mechanism oi'the free-vane class, a diiferential gear train for operativelyassociating the two for control purposes, and a common scale forindicating the relation between the set value of the control system andthe actual value of the controlled variable, together .with a recordingmechanism whereby may be obtained a permanent record of all valuesattained by said variable over a period of time. v

Mounted in the framework i0 is an extended slide-wire structure I I,iorming a part of a conventional potentiometer circuit, as shown in Fig.2 wherein a battery I! supplies a constant current through saidslide-wire in series with rheostat i3 made adjustable for the purpose ofstandardizing the slide-wire current to a predetermined value. A contactit is adapted to translate along the slide-wire II, and isborne by acarriage i 5 free to travel on guide rails l6 attached to the frameworkIll, whereby said carriage and contact may be givenfmotion parallel tothe extended length of said slide-wire structure by means of a leadscrew ,ll threadedly engaging the carriage i5.

An oven or furnace I8 is adapted to be heated by .the combustion of afluidfuel admitted to a said galvanometer being connectedby means of aconductor 25 to the contact It;

A reversible electric motor 26 operatively attached to the lead screw I1is adapted to be driven in either direction according to the alternativeenergization of its two windings 21 and 28, thereby translating thecarriage l5 along the .guide rails Hi, and the contact it along theslidewire II. The galvanometer 24 has a pointer 29 carrying a contact30, which may engage either of two stationary contacts Hand 32 accordingto the; sense of deflection of the galvanometer. Con tacts 3| and 32 areconnected to the'windings 2i and 28 respectively of themotor 28 by meansof conductors 33'and34. The windings 21 and 28 have a' common point 35which, by means of a conductor 36, is connected to one side of an andthe galvanometer.

electrical power supply 31, and the other side of said supply isconnected by means of a conductor 38 to the movable contact 30 of thegalvanometer.

tween their respective radii. Fixed to the spindle Characteristics andpolarities of the potentiometer and control circuits are so chosen thatthe mechanism continually tends to position the contact 14 along theslide-wire H in a sense to reduce to zero the total value of E, M. F.existing in the circuit which includes the thermocouple An index 39mounted on the carriage l cooperating with a stationary graduated scale40 provides a measure of the position of the contact Hi with respect tothe slide-wire, and therefore of the E. M. ER, and thus of thetemperature, of the thermocouple 2|. For the instrument, as thus fardescribed, no invention is claimed; and full equivalents therefor, andto which the invention may readily be adapted, are found in U. S.Letters-Patent No. 2,082,109, issued September 29, 1936, to O. H. Hunt,and in co-pending application Serial No. 363.275, filed October 29, 1940by F. B, Bristol.

The pneumatic regulating mechanism by which the position of the valve iscontrolled may advantageously be of the type set forth in U. S.Letters-Patent No. 1,880,247 to H. L. Griggs and A. R. Mabey, grantedOctober 4, .1932, wherein a thin movable vane tends variably to obstructthe escape of airfrom a pair of opposed Jets or orifices, therebyaffecting the back pressure and controlling the action of a diaphragmvalve.

- As herein set forth a thin metallic vane M is fixed to a rotatableshaft 42 and swings freely between opposed jets Q3 of a divided orificemember 44. The orifice member M receives compressed air through aconduit 45, having therein a constriction 46, from a source of supplyA7. A bellows member 48 communicating with the .conduit is adapted torespond through a limited range in its longitudinal dimension tovariations in pressure within said conduit. A double-seated pilot valve49 of the supply-and-waste type is provided with an internal cavity 56containing a seating member 5| actuated from the 'bellows member 58 bymeans of a stem 52 whereby it may be made to engage alternatively eitherof two seat portions 53 and 54. A conduit 55 admitsair from the supply4! through the seat portion 53 to the cavity 50, and an annular spacesurrounding the stem 52 provides communication between the cavity 50 andthe external atmosphere through the seat portion 54. The seating member5|, as it is moved alternatively into juxtaposition with the seatportions 53 and 54 affects the communication of the cavity 50 relativelywith the atmosphere and the source of supply, thereby controllablyvarying the pressure in said cavity, A conduit 56 provides connectionbetween the cavity 50 and the diaphragm top of the valve 20, therebycommunicating to said valve the pressures developed in said cavity andrendering the valve controllable by the pilot valve 49, and thus subjectto the position of the vane M.

A differential gearing 51 includes two main bevel gears 58 and 59 and aplanetary member 60 having pinions engaging both said gears, saidplanetary member being fixed to a rotatable shaft 61. Attached to theshaft BI is also a cam member 62 having toward the extremities of itsworking face two arcuate portions 63 and 64, the radius of the formerportion being materially greater than that of the latter, and a spiralportion 65 subtending an angle between said arcuate portions and forminga smooth transition be- 42 is a lever arm 56, carrying a roller 5'1which engages the face of the cam 62, constituting a follower therefor,whereby the'angular position of the spindle 42 and thus of vane M ismade de pendent upon that of the cam, and therefore of the planetarymember 80.

Mounted integrally with the bevel gear 58 of the differential train 51,and free for rotation therewith about the shaft El, is a spur gear 58.An idler comprised of a pinion 58 and a gear 68 integrally mounted isfree for rotation about a fixed spindle ill on the frame ID, the pinion68 meshing with the gear'58, and the gear 68' meshing with a pinion 69carried by the shaft of the lead screw ll. Mounted integrally with a thebevel gear 59 and free for rotation therewith knob 13.

about the shaft 6! is a spur gear 59 meshing with a pinion 7G fixed to ashaft 'H rotatably mounted in the framework l0 and positioned adjacentthe scale M! and parallel to the guide rails l6. Rotation of the shaft His adjustably effected by means of a worm gearing 12 adapted for manualoperation by means of a knurled Fixed to the'shaft II is a traversingscrew 14 threadedly engaging a nut 15 free to travel on a guide rail 16parallel to the guide rails It. The nut 15 carries an index i1 whichcooperates with the graduated scale Ml to provide an indication of theadjusted position of the shaft H, and therefore of the gear 59 of theplanetary train.

The ratios of the gears associated with the differential train and therelative pitches of the lead screw I! and the traversing screw 14 are soselected that the magnitude of angular displacement imparted through thegear 58 to the planetary member 60, the shaft 6! and the cam member 62,by rotation of the lead screw 11 to move the index 39 a certaindistancealong the scale 50, will be exactly neutralized by the angulardisplacement imparted through the gear 59 and the pinion 70 from thetraversing screw it by rotation of said screw through an anglesufficient to move the index ll an equal distance along said scale.

The cam member is so proportioned that when in a position of balance,corresponding to identity of indication of the indices 39 and 17, thefollower 67 will lie on the spiral portion 55 of its working face,.whereby any departure of the indices ll and 39 from identity ofindication will cause the arm 66 to be angularly displaced, therebyeffecting motion of the vane a: with respect to the opposed jets of theorifice member 44.

The radii of the arcuateportions 63 and 64 of the cam face are such thatwhen the follower 51 rests in engagement with either of these, the vanell will be positioned at the corresponding extreme of its working range,and of cours will not change its position so long as thefollower doesnot engage the spiral face. In order that the cam follower shall remainon the periphery of the cam whatever the relative position of theindices 39 and Ti, the over-all circumferential length of the camcontour is made to correspond to slightly more than twice the wholerangeof travel of the carriage or the nut. By proportioning the anglesubtended by the spiral portion 65 described being of --the .throttlingtype, it will be apparent that under different conditionsdemandingdifierent rates of flow of fuel through the valve 29 this valv willrequire to be operated atdifierent settings, and hence, the cam follower61 will require tolie at diflerent positions on the spiral part of theperiphery of cam 63. Such be-' ing the case, it is obvious thatidentityof indication between the indices 1'! and 39 can be obtained only withone certain position of the valve 20, and that for other positions ofthis valve there will be a difference in the indication of the twopointers, depending in its magnitude upon the width of the throttlingrange represented by the spiral part of cam 83.

For the purpose of explaining the complete operation of the instrumentembodying the invention, it may be assumed that ther has been at-'tained a steady-state condition, in which admission of fuel to theburner I9 is just suflicient to maintain the oven [8 at a constanttemperature.

The potentiometer mechanism, subject to the galvanometer 24 and themotor 26, will have set the carriage IS in a position where the E. M. F.

derived from the slide-wire II by the contact M will serve to balancethat developed in the thermocouple 2|, reducing to a zero value thetotal Theposi- E. M. F. in the thermocouple circuit. tion ofthe'carriage will be indicated on the scale 40 by the index 39, thusproviding a measure of.

the thermoelectromotive force developed by the couple, and therefore ofthe temperature within the oven l8. Under one such conditioncorresponding to a selected position of the valve the index 39 willcoincide with the index 11 in respect to the scale and under thiscondition the vane th electrical equilibrium in the potentiometer systemand causing a deflection of the contacting galvanometerz l, which,acting through the motor 26 and the lead screw I! as hereinbefore setforth, will cause the contact I '4 to apprqach'a new balance position onthe slide wire, the extent of movement being measured by the deflectionof I the index 39 and its departure from the indication ofthe index TI.The rotation of the lead screw I! will be transmitted to thediiferential train; and, the angular displacement of the gear 58 notbeing neutralized by movement ofthe'gear 59, the planetarymember 60 andthe cam member 62 will be angularly displaced, the movement of thespiral portion 65 with respect to th cam follower 61 serving to shiftthe lever arm 66 and the vane 4|, thus changing the back pressure of airin the conduit 45.

The changed air pressure in the conduit will be communicated to thebellows'48, changing the setting of the three-way valve 49 and changingthe pressure on mediaphragm valve 29, whereby the latter will tend toassumea new setting adapted to the admission of the required increase ofrate of fuel supply to the burner l9. As hereinbefore pointed out, thechanged demand for fuel may result in the finally attained temperaturediil'ering somewhat from the setting or the index 11; and where thisdeviation-is of a magnitude greater, than that permit- I ted by therequired precision of control, there may be applied one of several formsof resetting devices which, by coacting with the vane 4|, willcompensate for the deviations and maintaining a "straight line control.Examples of such devices are set forth in the co-pending applica'tlonSerial No. 174,609, filed by C. W. Bristol, November 15, 1937.

Should the demand for fuel be reduced, as'indicated by 'anincrease inoven temperature, the reaction will be, carried, in a manner similar tothat hereinbefore set forth, back through the potentiometer system, thedifferential gear train,

the cam member and the pneumatic control to the fuel valve, establishingthe fuel supply at the required lower value.

The preceding explanation applies to conditions where it is requiredthat the temperature" be maintained at a predetermined constant value.Where 'it is required that this value, (commonly known as the controlsetting be changed, the

shaft H is rotated by manual operation of the worm gearing 12 by meansof the knob 13, thus,

through the pinion 'Illand the gear 59, positioning the planetary memberand the cam member 62 in a position to move the vane 4| from its normalcontrol-position, the positions of elements corresponding to the changedcondition being indicated by the index 11 on the scale 40. I

The disturbance of equilibrium in the pneumatic system occasioned by thechange in position of the vane 4! will, according to actions herelnbe-26 to rotate the shaft of the lead screw I! to an fore set forth, actthrough the pilot valve 49 and the control valve 20 to change the rateof admission of fuel to the burner l9, with a consequent change intemperature in the oven l8.v The changed temperature, influencing thethermocouple 2I and the associated potentiometer and electrical controlcircuits, will cause the motor extent that the difierential gearing,actuated through the idler 68 and the gear- 58, will tend to reset thecam member 62 to an angular position corresponding to the setting of thevane ll at which there will be admitted to the furnace suflicientheating agent to maintain the newly established condition. Asequilibrium is approached at the new setting, the temperature attainedwill be indicated by the position'of the index 39 with respect to thescale 49. As hereinbefore pointed out, the action in the controller.

may be such as to attain a condition of balance with a slight deviationfrom the established setting of the index 11; but by proper selection ofthe throttling range or by the use of a suitable resetting device, thisdeviation may be reduced to a negligible magnitude or entirelyeliminated. Such devices do not form apart of the present invention.

It may be noted'that the arm 66 (Figs. 2 and 4) is constrained by itsweight (or by a suitable spring) to maintain the roller 61 against theperiphery of cam 62. The reaction between the roller 61 of arm 66, andthe cam surface with which it engages, develops such torque of the camabout its axis of rotation as to eliminate back I lash in the associatedgearing.

A record of temperatures measured by the thermocouple 2| over a periodof time may be obtained by means of a feed-roll 19 mounted in the frameand rotated about an axis parallel to the path of said carriageat aconstant speed,

as by a clock, and bearing a continuous sheet of chart paper I9 uponwhich a stylus or pen 80 provides a graph of all positions assumed bythe carriage l5.

In the servicing of instruments involving measuring circuits andcontrolapparatus of the classes set forth, it is highly important that it bepossible to obtain access to all parts of the mechanism for observationand adjustment while the instrument is operating in a normal manner. Theconstruction or an instrument involving all the elements hereinbeforeset forth, in a form wherein all parts would be accessible from thefront, would result in a unit occupy a prohibitive amount of panelspace, and otherwise being of undesirable proportions. It becomesnecessary, therefore, that the operating mechanism be of considerabledepth, and that provision be made for removing it from its casing sothat elements located toward the rearward parts of the assembly or onthe ends would be readily accessible for examination and detailedservicing.

Various more or less efiective expedients for this purpose have beendeveloped, the most common being that of hinging the operating mechanismwithin its case to swing about a vertical axis. In instruments of thisclass wherein pneumatic control-has been embodied, it has heretoforebeen the practice, partly because of the massive nature of the mechanisminvolved, and partly because of the difliculty in providing flexibleconnections to handle the relatively large volume of air required by thecontrol systems employed, to aflix the pilot valve or its equivalent tothe interior of the case and provide a mechanical connection with theswingable part normal operation when the instrument is opened forinspection. I

Referring to Fig. 1, the framework I which supports all the operativeparts of the instrument as hereinbefore enumerated, is itself carried bya pair of hinges 8| and 82 disposed about a common vertical axis andmounted within and at one end of a casing 83 adapted to contain saidframework and all parts carried thereby. The casing 83 may be supportedin any conventional manner, as by resting upon a flat horizontal surfaceor by being suspended by lugs 84 from a suitable vertical surface orpanel. Included in the conduits l and 56 are flexible sections '85 and,"which may be fabricated from any suitable metallic or non-metallictubing material. It is understood, moreover, that the electricalconductors, including the wires 36 and 38 communicating with the sourceof power for operating the potentiometer balancing mechanism, and thethermocouple leads 22 and 23, may also include flexible portions topermit of unhampered movement of the mechanism about the hinges BI and82.

When operating normally, the mechanism of the instrument, carried by theframework In, is wholly within the case, the frame being secured inposition by suitable fastening means, as a screw 81 threadedly engaginga lug 88 within the case. When it is desired to open the instrument forinspection, the screw 81 is released and the whole-mechanism swungoutward about the axis of the hinges 8| and 82 until all parts areaccessible; and as the flexible connections provided maintain thepneumatic and electrical circuits, uninterrupted operation of allpartsmay continue to be effected ina normal manner.

In Fig, 5 is shown a modification of the inven-' tion, whereby itsprinciples may be adapted to the purposes of electrical control. The arm66 carries, instead of a vane, a rheostat-arm 89 adapted to cooperatewith a resistor element 90 connected. in circuit between a heatingelement SI and a source of electrical energy 92. The thermocouple 2|being placed in a space to be heated-by the element 9|, control will beeiiected through the instrumentalities as hereinbefore de-' scribed; therheostat arm 89, by its position with respect to the resistance 90,serving to control the magnitude of current flowing in the element SI,and thus to regulate the temperature to whichthe thermocouple 2i isexposed.

The terms and expressions which I hav em ployed are used as terms ofdescription and not of limitation, and I have 'no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but reco nize thatvarious modifications are possible within the scope of the inventionclaimed.

I claim:

1. In an instrument for measuring and controlling the magnitude of avariable condition, means sensitive to changes in said magnitude, afirst deflecting member adapted by its deflection to provide a measureof said magnitude, a first rotatable element controlled by saidsensitive means for positioning said member along a given path, a seconddeflecting member positionable along a path parallel to thefirst-mentioned path to positions corresponding to desired magnitudes ofsaid condition, a second rotatable element operable concurrently withthe positioning of said second deflecting member, a diflerential gearingcomprising two main gears and a planetary member adapted to partake ofthe resultant motion. of said main gears, one of said main gears beingconnected to the first rotatable element for rotation thereby, and theother of said main gears. being connected to thesecond rotatable elementfor rotation thereby, and means controlled by said planetary member forregulating said variable condition.

2. In an instrument for measuring and controlling the magnitude of avariable condition, means sensitive to changes in said magnitude, afirst deflecting member adapted by its deflection to provide a measureof said magnitude, a first rotatable element controlled by saidsensitive means for positioning said member along a straight path, asecond deflecting member positionable along a path parallel to thefirst-mentioned path to positions corresponding to desired magnitudes ofsaid condition, a second rotatable V element operable concurrently withthe positioning of said second deflecting member, a differential gearingcomprising two main gears and a planetary member adapted to partake ofthe resultant motion of said main gears, one of said main gears beingconnected to the first rotatable element for rotation thereby, and theother of said main gears being connected to the second:

g I l r 2,826,238 rotatable element for rotation thereby, and meanscontrolled by said planetary member for regulatme said variablecondition.

3. In an instrument for measuring and controlling the magnitude of avariable condition,

. means sensitive to changes in said magnitude, a

first deflecting member adapted by its deflection to provide a measureof said magnitude, a first rotatable element controlled by saidsensitive means for positioning said member along agiven along a pathparallel to the first-mentioned path path, a second deflecting memberpositionable to positions corresponding to desired magniof said seconddeflecting member, a diiierential gearing comprising two main gears anda planetary member adapted to partake of the resultant tudes of saidcondition, a second rotatable element operable concurrently with thepositioning motion of saidmain gears, one of said mean gears beingconnected to the first rotatable element for rotation thereby, and theother of said main gears being connected to the second rotatable elementfor rotation thereby, cam means operated by said planetary member, andmeans cooperating with said cam means for controlling said variablecondition.

4. In an instrument for measuring and con- .trolling the magnitude ofavariable condition,

means sensitive to changes in said magnitude, 9.

first deflecting member comprising a threaded nut displaceable topositions corresponding to changes in said magnitude, a first-rotatableelement comprising a screwshaft controlled by said sensitive means andengaging said nut to position the latter axially along said shaft,asecond deflecting member comprising a threaded nut, a

second rotatable element comprising a screw shaft engaging thesecond-mentioned nut and manually operable to shift the same axially topositions corresponding to desired magnitudes of said condition, adifferential gearing comprising two main gears and a planetary memberadapted to partake of the resultant motionof said main placeable topositions corresponding to changes in said magnitude, a first-rotatableelement comprising a screw shaft controlled by said sensitive means andengaging said nut to position the latter axially along said shaft, asecond deflecting member comprising a threaded nut, a second ro-"tatable element comprising a screw shaft engaging the second-mentionednut and manually op-' erable to shift the same axially to "positionscorresponding to desired magnitudes of said condition, a difierentialgearing comprising twomain gears and a planetary memberadapted topartake of the resultant motion of said main gears, one of said maingears being connected to the first rotatable element for rotationthereby, and the 7 other of said main gears being connected to thesecond rotatable element for rotation thereby. cam means operated bysaid planetary member, means cooperating with said cam means for controlling said variable condition, said screw shafts being substantiallyparallel to each other, a scale extending substantially parallel to saidscrew shafts, and indicating elements positioned by the respectivenutsfor cooperation with said scale, the deviation between the positionsof said in-' dicating elements on said scale corresponding to theposition of said cam means.

6. In an instrument for measuring and con-- trolling the magnitude of avariable condition, means sensitive to changes in said magnitude, a

graduated surface, a first deflecting member juxtaposed to said surfaceand adapted to provide thereon a measure of said magnitude, a first ro-'tatable element controlled by said sensit ve means for positioning saidmember with respect to the graduations on said surface, a seconddeflecting member juxtaposed to said surface and adapted to provide inconjunction with the graduations thereon measures corresponding todesiredmag- Initudes of said condition, a second rotatable elementoperable concurrently with the positioning of said second deflectingmember, a differential gearing comprising two main gears and a planetarymember adapted to partake of the resultant motion of said main gears,one of said main gears being connected to the first rotatable elementfor rotation thereby, and the other of said main gears being connectedto the second rotatable element for rotation thereby, cam means operatedby said planetary member, and means cooperating with said cam means forcontrolling said variable condition.

